Generally, the optical memory card is a plastic card and can record and read data in its recording region with a laser beam.
FIG. 6 shows a recording region 102 of an optical memory card 101. As shown in its enlarged diagram, data recording tracks 103 for recording information and guide tracks 104 formed at given intervals to control tracking for stabilizing a radiating position of the laser beams for recording and reading are alternately disposed on the recording region 102.
The data recording tracks 103 and the guide tracks 104 have a different reflection ratio. The data recording tracks 103 have a reflection ratio higher than the guide tracks 104 do.
And, a record pit 105 is a portion having a low reflection ratio, which is formed in the data recording tracks 103, with the laser beam when information is recorded. The presence or not of the record pit 105 indicates information recorded.
FIG. 7 shows a logical data structure of the recording region 102. On the recording region 102, in addition to a sector 120 where information is recorded, read-in 121 from which bit synchronization is obtained and an SYNC mark 122 from which frame synchronization is obtained by a non-illustrated optical memory card reader/writer when recording or reading and BOS 123 required for detecting a start position of the sector 120 are recorded.
The read-in 121 has the SYNC mark 122 recorded and record pits 105 formed at recorded intervals.
An optical memory card reader/writer (not shown) is provided with a synchronization signal generator (not shown), scans the optical memory card 101 at a scan rate so that a synchronization signal output from the synchronization signal generator agrees with a signal which rises for every one bit detected by scanning the read-in 121, and keeps the same scan rate to have bit synchronization.
And, a modulation system which includes a synchronization signal into information to be recorded may be adopted to extract the synchronization signal from the signal detected when reading, in order to firmly retain the obtained bit synchronization.
The SYNC mark 122 is formed of record pits 105, which are arranged in a pattern not produced by modulation, and used when the non-illustrated optical memory card reader/writer gets frame synchronization.
The frame is a bit separation to process a signal by a signal processing circuit in the non-illustrated optical memory card reader/writer. The non-illustrated optical memory card reader/writer is provided with a counter (not shown) for obtaining frame synchronization. The counter counts the synchronization signal, outputs a frame synchronization signal after counting up to the number of bits configuring one frame, and resets its counted number.
Since the SYNC mark 122 is recorded at the start end (or termination end) of the frame, the non-illustrated optical memory card reader/writer scans the optical memory card 101. And when the SYNC mark 122 is detected, the number indicated by the non-illustrated counter for obtaining frame synchronization is reset, thereby assuring the acquisition of frame synchronization.
Description will be made of a procedure for recording data on the optical memory card.
A non-illustrated memory card reader/writer scans the optical memory card 101 to obtain bit synchronization by the read-in 121 and frame synchronization by the SYNC mark 122. Then, the non-illustrated optical memory card reader/writer generates a write signal according to data to be recorded and enters the signal into a non-illustrated optical head. The optical head forms a record pit 105 on the data recording track 103 according to the write signal.
After recording all data, the non-illustrated optical memory card reader/writer reads the recorded data to compare it with data to be recorded. If they agree with each other, the recording operation is terminated, but if not, it is determined as recording error, and the recording operation is repeated from the beginning.
The recording error occurs frequently when synchronization between a card carrying velocity and an electric circuit (bit synchronization, frame synchronization) is lost due to interference such as vibrations on the non-illustrated optical memory card reader/writer during the recording operation.
FIG. 8 shows an example of the record pit 105 which is formed on the data recording track 103 if synchronization is lost.
In FIG. 8, a data recording track 103-1 has the record pits 105 formed normally, but a data recording track 103-2 has the record pits 105 formed with irregular intervals and some of them are overlaid with the SYNC marks 122 because synchronization was lost.
Data recorded on the data recording track 103-2 is not read normally. Therefore, it is rerecorded on another data recording track 103.
However, the data recording method described above cannot rerecord data on the portion where a recording error has occurred, resulting in a disadvantage that the recording capacity of the optical memory card as the whole is lowered.